“There are more buyers than sellers,” said Seattle real-estate economist Matthew Gardner. “Buyers are getting frustrated with their agents, because they can’t show them what they want.”

The total number of houses for sale in King County in September was down 36 percent year-over-year in September, according to the listing service. Condo listings were down a whopping 50 percent.

Inventory hasn’t been this scarce since at least 2000, said blogger Tim Ellis of Seattlebubble.com. “There’s nothing to choose from.”

The lack of inventory is suppressing sales, he said.

Even so, 2012 so far has been the best year for sales volume since the real-estate bust in 2008. Buyers are looking again, lured back to the market by record-low mortgage interest rates, rising rents and home prices that appear to have stabilized.

But the bust still is exerting some influence. Experts blame the lack of inventory in part on homeowners who bought just before the peak in summer 2007 and now can’t afford to sell. They owe lenders more than their homes are worth.

Both closed and pending sales were down in September from August, but that is the typical seasonal pattern.

Southeast and Southwest King County — where houses are most affordable and foreclosures and short sales are most prevalent — both saw double-digit year-over-year price increases last month. The median sale price jumped nearly 20 percent in Southeast King County — Renton, Kent, Auburn and points east — climbing from $225,000 to $269,950.

Prices on the Eastside and in North King County, in contrast, were flat. Prices rose nearly 8 percent in Seattle.

The South End’s big price increases most likely reflected a drop in sales of bank-repossessed homes, according to data compiled by online brokerage Redfin.

Bank-owned houses made up 36 percent of all sales in Southwest King County and 28 percent of all sales in Southeast King County in September 2011, according to Redfin.

Last month, those percentages dropped by more than half, to 19 and 12, respectively.

Southeast King County’s for-sale inventory of “distressed” homes — those owned by banks, or offered as “short sales” for less than sellers owe lenders — has been falling for several months, Gardner said, while the “non-distressed” inventory has been climbing.

As non-distressed homes make up a bigger share of sales, he said, the county’s southern reaches are enjoying increases in median sale prices that Seattle and the Eastside experienced earlier.

Countywide, bank-repossessed houses accounted for less than 8 percent of all sales last month, Redfin said, down from 18 percent in September 2011.

The Eastside saw the biggest bump in closed sales last month, up 21 percent from September 2011. Sales volume actually declined 1 percent in Southwest King County.

The King County condo market fared even better than the single-family market in September, at least in comparison with the same month in 2011. Condo sales volume was up 25 percent, while the median price jumped 10 percent, from $195,000 to $214,500.

Southwest and Southeast King County again experienced the biggest year-over-year price increases — 23 and 16 percent, respectively — while the median rose just 4 percent in Seattle and the Eastside.

In downtown Seattle and Belltown condos, however, the median price rose nearly 19 percent, to $409,000.

When distressed sales are excluded, the median price of condos sold downtown over the past three months is actually higher than it was during the same period in 2007 — before the crash, according to data compiled by brokerage Realogics Sotheby’s International Realty.

In Snohomish County, single-family home sales were up 7 percent year-over-year, while the median price jumped nearly 16 percent, to $280,000.